The outcomes of minimally invasive medical procedures can be improved by using electromagnetic tracking systems (EMTS) to track the location of medical instruments and display this information on medical images, thereby helping to guide the medical instrument to a target location in the anatomy. EMTS generally uses an electromagnetic field generator to create a local electromagnetic field at the site of the procedure and a medical instrument or device containing a suitable sensor coil. Electrical current is induced in the sensor coil which is a function of the position and orientation of the sensor coil relative to the electromagnetic field generator. The EMTS computes the position of the sensor coil, and therefore the position of the medical instrument, based on the induced electrical current. A particular advantage of EMTS is that line of sight is not required to determine/monitor instrument location or movement, thereby making it particularly suitable for tracking needles or catheters inside anatomy.
One of the main problems with using EMTS in a medical environment is the presence of metallic conductive or ferromagnetic objects in proximity to the electromagnetic field. These objects create distortions, or metal artifacts, which create errors in the position and orientation tracking of medical instrument(s). The table or platform capable of sustaining a medical procedure is usually a main source of metal distortions. However, other objects, such as CT gantry, X-ray or C-arm, can also cause and/or contribute to distortions. Such distortions and associated errors in a clinician's assessment/understanding of instrument positioning may directly and negatively affect the outcome of a medical procedure using EMTS. Currently the clinical utility of EMTS is limited because the positional and orientational accuracy of EMTS cannot be guaranteed in the presence of metal distortions.
U.S. Pat. No. 6,400,139 to Khalfin et al. discloses methods/apparatus for electromagnetic position and orientation tracking with distortion compensation functionality. More particularly, the Khalfin '139 patent discloses methods/apparatus that employ at least one stationary sensor, called a “witness sensor,” having a fixed position and orientation near or within the volume to account for electromagnetic distortion. One or more probe sensors are placed on an object to be tracked within the volume, and the output of each witness sensor is used to compute the parameters of a non-real effective electromagnetic source. The parameters of the effective source are used as inputs to the computation of position and orientation as measured by each probe sensor, as if the object were in the non-distorted electromagnetic field produced by the effective source or sources.
Despite efforts to date, a need remains for systems and methods that effectively compensate for metal distortions, thereby improving the accuracy and/or reliability of EMTS in a medical/clinical environment. In addition, a need remains for systems/methods that improve EMTS performance such that catheter tracking in cardiac and vascular applications, oncology applications such as needle biopsies, radio-frequency ablations, cryoablations, prostate cancer therapies, etc., are effectively and reliably achieved. These and other needs are satisfied by the systems and methods disclosed herein.